Re: Map function which adds last two numbers of a list

• To: mathgroup at smc.vnet.net
• Subject: [mg73578] Re: Map function which adds last two numbers of a list
• From: "dimitris" <dimmechan at yahoo.com>
• Date: Thu, 22 Feb 2007 04:34:09 -0500 (EST)
• References: <ergqrb\$jg0\$1@smc.vnet.net>

```Hi.

Along many other alternatives you can try

In[119] := z /. {x_, y_, z_, w_} :> {x, y, z + w}
Out[119] = {{1, 4, 11}, {7, 8, 10}, {1, 2, 7}}

In[120] := ({#1[[1]], #1[[2]], #1[[3]] + #1[[4]]} &) /@ z
Out[120] = {{1, 4, 11}, {7, 8, 10}, {1, 2, 7}}

In[216]:=
{z[[#, 1]], z[[#, 2]], (Plus @@@ Reap[{Sow[#[[3]]], Sow[#[[4]]]} & /@
z][[1]])[[#]]} & /@ Range[3]

Out[216]=
{{1, 4, 11}, {7, 8, 10}, {1, 2, 7}}

However pay special attention to what Andrzej Kozlowski mentions you
in his post!

Dimitris

=CF/=C7 Christopher Pike =DD=E3=F1=E1=F8=E5:
> Hi,
>   Consider this:
>
> z = {{1,4,5,6},{7,8,9,1},{1,2,4,3}}
>
> I'd like to Map a function onto z which would replace the last two items
> with their sum:
>
> {{1,4,11},{7,8,10},{1,2,7}}
>
> I could easily use the Table command to construct this new table, but it
> would be nicer if I new how to Map some function on z that would produce
> the same result.
>
> Any suggestions.
>
> Thanks, Chris Pike

```

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